While aspects of this disclosure apply to any engine that requires a human to insert a feeler gauge or otherwise mechanically set and adjust valve clearances by hand, the currently understood valve adjustment procedure for the 1965 to 1994 Porsche® 911 engines is used as a basis for the description of various embodiments of the present disclosure. On the pre-1995 Porsche® 911 engine, setting and adjusting the valves is currently performed in several different ways and using several different tools, but always by turning an adjustment screw located in the rocker arm and, once the specified clearance is set, locking the screw down with a lock nut. This process is very difficult to perform with the engine in the car given the small clearances, lack of visibility and manipulation of tools around the engine parts and compartment. The process is still difficult to perform even with the engine out of the car because the tolerances for the adjustment are very small. For example, in the aforementioned Porsche® 911 engines, the gap between the swivel foot of the adjustment screw and the valve stem is specified by the manufacturer at 0.1 mm.
Further, because there are two valve adjustments (an intake and an exhaust) for each of the 911's six cylinders, the process must be repeated 12 times. Even then, because the known procedures are not simple or accurate, it is typically recommended that all clearances be checked twice or even three times before completing the valve adjustment process. The entire process can take several hours for a skilled mechanic and up to two days or more for an unskilled mechanic. Even then, because the process requires human “feel” for the gap at issue and the tightening of the lock nut without movement of the adjustment screw, the actual results obtained can be questionable, even for a skilled mechanic familiar with these types of engines.
For example, with respect to the 911 engine, there are several different known methods of adjusting the valves. Each employs the factory or original equipment manufacturer (OEM) type adjustment screw and a lock nut. The traditional method of valve adjustment is well-described in other publications and the original factory manuals for the engines described. For the 911 engine and with reference to FIG. 1, the traditional method involves loosening a lock nut 100 and inserting a 0.1 mm feeler gauge (not shown) into a very small gap 104 between a swivel foot 108 of an adjustment screw 112 and a valve stem 116. Once in place, adjustment screw 112 is turned until the feeler gauge can barely be removed from gap 104, and then lock nut 100 is tightened down onto a rocker arm 120 with the feeler gauge in place while the adjustment screw is held in place relative to the rocker arm with a screwdriver. This is very difficult to accomplish even for those with experience and especially on the rocker arms located in the back of the 911 engine, such as the rocker arms associated with cylinder number six. One 360-degree radial turn of adjustment screw 112 results in 1 mm of axial travel of swivel foot 108. Thus, the traditional factory-recommended adjustment process for the 911 engine involves ensuring that once gap 104 is set appropriately with the feeler gauge, adjustment screw 112 does not rotate during the lock nut tightening step. This is difficult to achieve even with the engine out of the car, as noted above.
The “backside” method of valve adjustment is also well-described elsewhere, but, for the 911 engine, involves loosening adjustment screw 112 and then inserting a 0.0025 inch feeler into a space between a camshaft lobe (not shown) and a contact surface of the rocker arm at issue. Adjustment screw 112 is then tightened down so that the feeler gauge can barely slip out and then lock nut 100 is tightened down. The “feel” for doing this is subjective. Once the adjustment is locked, if a 0.003 inch feeler gauge cannot fit in the space between the camshaft lobe and the rocker arm contact surface but the 0.0025 inch feeler can, then the spacing of gap 104 is 0.1 mm. The backside method requires removal of engine shrouding surrounding the engine and some exhaust system components and is very difficult to perform on some hard-to-reach cylinders.
Kirk Engines, Inc. has developed a tool (not shown) that operates without a feeler gauge on the principle that turning adjustment screw 112 one tenth of a full radial rotation achieves the desired axial gap of 0.1 mm. First the tool is placed over a 13 mm box end wrench that has been placed on lock nut 100. Then, with the tool, one screws down adjustment screw 112 until contact is made between swivel foot 108 and valve stem 116. The user then moves a pointer to a designated mark on the tool. The user then uses the knurled knob on the tool to rotate engaged adjustment screw 112 counterclockwise to another designated mark that corresponds to 1/10 of a full rotation. This achieves the desired 0.1 mm gap between swivel foot 108 and valve stem 116. Now, the user must hold the Kirk tool in place without moving the knurled knob and using the box end wrench, tighten lock nut 100 down without rotating adjustment screw 112. This is cumbersome and very difficult to accomplish with only two hands in very close quarters and with limited visibility.
Another less often used method of adjusting valves is to employ the use of a Stomski Racing or other jigs and a dial gauge indicator. While providing good accuracy through the use of the dial gauge, this method requires a lot of set up and tear down for each valve, is very hard to set up with the engine in the car given cramped space conditions, and requires expensive tools and a skilled mechanic who has developed a “touch feel” for locking down lock nut 100 while holding adjustment screw 112 in place. This method also requires trial and error adjustments until gap 104 is set to the appropriate spacing and then confirmed with the dial gauge.
The net result of the existing methods of valve adjustment is unsatisfactory. The adjustment is hard to achieve, often inaccurate, not always replicable, and always difficult to perform. As a consequence, some owners spend many hours performing the valve adjustment that is recommended to be performed every 15,000 miles on the 911 engine as normal maintenance. Rechecking and adjustment of the valve clearances is recommended at certain intervals because the valve seat will wear over time and impact the size of gap 104. Further, lock nut 100 can loosen and, thus, allow adjustment screw 112 to move out of the set position. Many owners opt to have a mechanic perform the adjustment at the cost of upwards of $500, and even then the ability of mechanics to achieve the requisite tight tolerances is questionable.
Improperly set valves can damage the engine resulting in thousands of dollars in repair costs and, at the least, cause an otherwise well-engineered and powerful car to perform at well less than optimal levels. The need for a reliable, consistent, replicable, easy, and accurate valve adjustment mechanism has long been sought and desired for the 911 engine and any other engine that features a rocker arm and mechanical valve adjustment screw mechanism.